This invention relates to absorbent products and more particularly to products used for absorbing and retaining body fluids and worn in contact with the body such as diapers, sanitary napkins, dressings and the like.
In general, such products comprise one or more layers of a core of hydrophylic material such as wood pulp, rayon, gauze, tissue or the like and in some cases, synthetic hydrophilic material such as hydrophilic polyurethane foam. The hydrophilic material is generally provided in the form of a pad, usually having a rectangular shape and enveloped in a cover which can be a woven material such as gauze or a non-woven fabric. The cover is pervious to body fluids on at least the side of the product designed to be placed against the body. A body fluid impervious barrier sheet is generally provided on the opposite side of the pad, i.e., the side facing away from the body, in an effort to protect the clothing from staining and wetting.
The absorbent product is positioned on the body so that the body fluid being absorbed strikes the pad in a central area thereof and ideally, should then be evenly distributed by wicking action throughout the entire pad. The ideal situation of even distribution will make maximum use of the absorbent material in the product and thus, in theory, the outer surfaces will not be wet and the pad will not require changing until all of the absorbent material is saturated.
Unfortunately, the real situation is far from this ideal. In practice, fluid striking a major surface of a rectangular pad is first absorbed into the pad for a certain distance and then wicks radially in all directions. Since the width of the rectangular pad is less than its length, fluid wicking radially first wets an outer surface at the longitudinally extending side edges of the product. While this occurs long before the entire pad is totally saturated, once the edges of the product are wet, it is necessary to change the product even though only a small portion of the potential absorption capacity has been utilized.
Those skilled in the art, therefore, have directed their efforts toward solving this side leakage problem. One solution, employed with such products as disposable diapers and sanitary napkins, is to provide an impervious barrier sheet on the side of the pad facing away from the body, this sheet being sized wider than the pad, i.e., extending beyond the pad along each longitudinal edge. The wide edges are then folded to cover the longitudinally extending side edges of the pad and preclude the passage of fluid therethrough. Unfortunately, this construction imparts undesirable effects when the barrier sheet, normally a polymeric film, is placed against or in juxtaposition with the skin of the user for a significant length of time. This is due to the inherent nature of most commercially employed barrier sheets, e.g., polyethylene, which have extremely poor moisture vapor and gas transmission properties so that, in the areas where they contact the skin, they substantially inhibit moisture vapor transmission, thereby retaining moisture in contact with the skin and leading to irritation and the formation of rashes, etc.
An attempted improvement is described in U.S. Pat. No. 3,230,955 issued on Jan. 25, 1966 to C. G. Joa et al. wherein a barrier sheet is sandwiched between two layers of cellulosic material and then employed to cover the side of the pad facing away from the body and the longitudinal sides of the pad. Another cover is applied to fully overwrap the product. While the layers of cellulosic material and the overwrap do add to the comfort of the product, they do so by decreasing the effectiveness of the barrier sheet in preventing side leakage. This is because the cellulosic layer and the wrapping, having a high wicking rate for fluids, tend to transfer body fluids which wet the body facing side of the pad to the longitudinal sides of the pad thus frustrating the purpose of the barrier sheet.
The problem of side leakage and the concomitant problem of user comfort has also been addressed in U.S. Pat. No. 4,015,604 issued on Apr. 5, 1977 to Charles Csillag. In accordance with this disclosure, the longitudinal edges of the pad are impregnated with a hydrophobic material to create hydrophobic zones which retard fluid transmission to the outer edges of the pad. Buffer zones between the extreme longitudinal edges of the pad and the hydrophobic zones are provided to insure user comfort. While a product made in accordance with this patent functions well, certain drawbacks are associated therewith. Firstly, the application of the hydrophobic zones is a difficult and expensive processing step and adds significantly to the manufacturing costs of the product. Secondly, the requirement of buffer zones and hydrophobic zones subtract from the useful absorbent portion of the pad and hence reduce to a degree the overall efficient use of the absorbent material of the pad.
In view of the above-described shortcomings of the prior art, a need still exists for a product which alleviates the side leakage problem while still being comfortable in use.